refactor how balancer messages are handled

makes it so that failure to handle an enum variant produces an error at compile time

server/clientmanager.ts

@@ -229,39 +229,69 @@ function onBalancerDisconnect(conn: BalancerConnection) {
 	}
 }
 
-function onBalancerMessage(conn: BalancerConnection, message: MsgB2M) {
+async function onBalancerMessage(conn: BalancerConnection, message: MsgB2M) {
 	log.silly("balancer message: " + JSON.stringify(message));
-	if (message.type === "join") {
-		const msg = message.payload;
-		const client = new BalancerClient(msg.room, msg.client, conn);
-		connections.push(client);
-		client.on("auth", onClientAuth);
-		client.on("message", onClientMessage);
-		client.on("disconnect", onClientDisconnect);
-		client.auth(msg.token);
-	} else if (message.type === "leave") {
-		const msg = message.payload;
-		const client = connections.find(c => c.id === msg.client);
-		if (client instanceof BalancerClient) {
-			client.leave();
-		} else {
-			log.error(
-				`Balancer tried to make client leave that does not exist or is not a balancer client`
-			);
-		}
-	} else if (message.type === "client_msg") {
-		const msg = message.payload;
-		const client = connections.find(c => c.id === msg.client_id);
-		if (client instanceof BalancerClient) {
-			client.receiveMessage(msg.payload as ClientMessage);
-		} else {
-			log.error(
-				`Balancer sent message for client that does not exist or is not a balancer client`
-			);
-		}
-	} else {
+
+	/**
+	 * This is a type that maps the message type to the handler for that message type.
+	 *
+	 * Useful for handling enums that are discriminated by a string, like the ones generated by typeshare.
+	 */
+	type EnumHandler<T extends { type: string; payload: T["payload"] }> = {
+		[P in T["type"]]: (
+			instruction: Extract<T, { type: P; payload: T["payload"] }>
+		) => Promise<void>;
+	};
+
+	// the intersection type makes it so that it throws a compile error if all the enum variants aren't handled
+	const handlers: Record<MsgB2M["type"], unknown> & EnumHandler<MsgB2M> = {
+		load: async message => {
+			const msg = message.payload;
+			await roommanager.getRoom(msg.room);
+		},
+		unload: async message => {
+			const msg = message.payload;
+			await roommanager.unloadRoom(msg.room);
+		},
+		join: async message => {
+			const msg = message.payload;
+			const client = new BalancerClient(msg.room, msg.client, conn);
+			connections.push(client);
+			client.on("auth", onClientAuth);
+			client.on("message", onClientMessage);
+			client.on("disconnect", onClientDisconnect);
+			client.auth(msg.token);
+		},
+		leave: async message => {
+			const msg = message.payload;
+			const client = connections.find(c => c.id === msg.client);
+			if (client instanceof BalancerClient) {
+				client.leave();
+			} else {
+				log.error(
+					`Balancer tried to make client leave that does not exist or is not a balancer client`
+				);
+			}
+		},
+		client_msg: async message => {
+			const msg = message.payload;
+			const client = connections.find(c => c.id === msg.client_id);
+			if (client instanceof BalancerClient) {
+				client.receiveMessage(msg.payload as ClientMessage);
+			} else {
+				log.error(
+					`Balancer sent message for client that does not exist or is not a balancer client`
+				);
+			}
+		},
+	};
+
+	const handler = handlers[message.type];
+	if (!handler) {
 		log.error(`Unknown balancer message type: ${(message as { type: string }).type}`);
+		return;
 	}
+	await handler(message as any); // this cast is safe because the type is checked and narrowed above
 }
 
 function onBalancerError(conn: BalancerConnection, error: WebSocket.ErrorEvent) {